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Message-ID: <20230316112832.2711783-4-libaokun1@huawei.com>
Date: Thu, 16 Mar 2023 19:28:32 +0800
From: Baokun Li <libaokun1@...wei.com>
To: <linux-ext4@...r.kernel.org>
CC: <tytso@....edu>, <adilger.kernel@...ger.ca>, <jack@...e.cz>,
<ritesh.list@...il.com>, <linux-kernel@...r.kernel.org>,
<yi.zhang@...wei.com>, <yangerkun@...wei.com>,
<yukuai3@...wei.com>, <libaokun1@...wei.com>,
<stable@...r.kernel.org>
Subject: [PATCH 3/3] ext4: fix race between writepages and remount
We got a WARNING in ext4_add_complete_io:
==================================================================
WARNING: at fs/ext4/page-io.c:231 ext4_put_io_end_defer+0x182/0x250
CPU: 10 PID: 77 Comm: ksoftirqd/10 Tainted: 6.3.0-rc2 #85
RIP: 0010:ext4_put_io_end_defer+0x182/0x250 [ext4]
[...]
Call Trace:
<TASK>
ext4_end_bio+0xa8/0x240 [ext4]
bio_endio+0x195/0x310
blk_update_request+0x184/0x770
scsi_end_request+0x2f/0x240
scsi_io_completion+0x75/0x450
scsi_finish_command+0xef/0x160
scsi_complete+0xa3/0x180
blk_complete_reqs+0x60/0x80
blk_done_softirq+0x25/0x40
__do_softirq+0x119/0x4c8
run_ksoftirqd+0x42/0x70
smpboot_thread_fn+0x136/0x3c0
kthread+0x140/0x1a0
ret_from_fork+0x2c/0x50
==================================================================
Above issue may happen as follows:
cpu1 cpu2
______________________________|_____________________________
mount -o dioread_lock
ext4_writepages
ext4_do_writepages
*if (ext4_should_dioread_nolock(inode))*
// rsv_blocks is not assigned here
mount -o remount,dioread_nolock
ext4_journal_start_with_reserve
__ext4_journal_start
__ext4_journal_start_sb
jbd2__journal_start
*if (rsv_blocks)*
// h_rsv_handle is not initialized here
mpage_map_and_submit_extent
mpage_map_one_extent
dioread_nolock = ext4_should_dioread_nolock(inode)
if (dioread_nolock && (map->m_flags & EXT4_MAP_UNWRITTEN))
mpd->io_submit.io_end->handle = handle->h_rsv_handle
ext4_set_io_unwritten_flag
io_end->flag |= EXT4_IO_END_UNWRITTEN
// now io_end->handle is NULL but has EXT4_IO_END_UNWRITTEN flag
scsi_finish_command
scsi_io_completion
scsi_io_completion_action
scsi_end_request
blk_update_request
req_bio_endio
bio_endio
bio->bi_end_io > ext4_end_bio
ext4_put_io_end_defer
ext4_add_complete_io
// trigger WARN_ON(!io_end->handle && sbi->s_journal);
The immediate cause of this problem is that ext4_should_dioread_nolock()
function returns inconsistent values in the ext4_do_writepages() and
mpage_map_one_extent(). There are four conditions in this function that
can be changed at mount time to cause this problem. These four conditions
can be divided into two categories:
(1) journal_data and EXT4_EXTENTS_FL, which can be changed by ioctl
(2) DELALLOC and DIOREAD_NOLOCK, which can be changed by remount
The two in the first category have been fixed by commit c8585c6fcaf2
("ext4: fix races between changing inode journal mode and ext4_writepages")
and commit cb85f4d23f79 ("ext4: fix race between writepages and enabling
EXT4_EXTENTS_FL") respectively.
Two cases in the other category have not yet been fixed, and the above
issue is caused by this situation. We refer to the fix for the first
category, When DELALLOC or DIOREAD_NOLOCK is detected to be changed
during remount, we hold the s_writepages_rwsem lock to avoid racing with
ext4_writepages to trigger the problem.
Moreover, we add an EXT4_MOUNT_SHOULD_DIOREAD_NOLOCK macro to ensure that
the mount options used by ext4_should_dioread_nolock() and __ext4_remount()
are always consistent.
Fixes: 6b523df4fb5a ("ext4: use transaction reservation for extent conversion in ext4_end_io")
Cc: stable@...r.kernel.org
Signed-off-by: Baokun Li <libaokun1@...wei.com>
---
fs/ext4/ext4.h | 3 ++-
fs/ext4/ext4_jbd2.h | 9 +++++----
fs/ext4/super.c | 14 ++++++++++++++
3 files changed, 21 insertions(+), 5 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 08b29c289da4..f60967fa648f 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1703,7 +1703,8 @@ struct ext4_sb_info {
/*
* Barrier between writepages ops and changing any inode's JOURNAL_DATA
- * or EXTENTS flag.
+ * or EXTENTS flag or between changing SHOULD_DIOREAD_NOLOCK flag on
+ * remount and writepages ops.
*/
struct percpu_rw_semaphore s_writepages_rwsem;
struct dax_device *s_daxdev;
diff --git a/fs/ext4/ext4_jbd2.h b/fs/ext4/ext4_jbd2.h
index 0c77697d5e90..d82bfcdd56e5 100644
--- a/fs/ext4/ext4_jbd2.h
+++ b/fs/ext4/ext4_jbd2.h
@@ -488,6 +488,9 @@ static inline int ext4_free_data_revoke_credits(struct inode *inode, int blocks)
return blocks + 2*(EXT4_SB(inode->i_sb)->s_cluster_ratio - 1);
}
+/* delalloc is a temporary fix to prevent generic/422 test failures*/
+#define EXT4_MOUNT_SHOULD_DIOREAD_NOLOCK (EXT4_MOUNT_DIOREAD_NOLOCK | \
+ EXT4_MOUNT_DELALLOC)
/*
* This function controls whether or not we should try to go down the
* dioread_nolock code paths, which makes it safe to avoid taking
@@ -499,7 +502,8 @@ static inline int ext4_free_data_revoke_credits(struct inode *inode, int blocks)
*/
static inline int ext4_should_dioread_nolock(struct inode *inode)
{
- if (!test_opt(inode->i_sb, DIOREAD_NOLOCK))
+ if (test_opt(inode->i_sb, SHOULD_DIOREAD_NOLOCK) !=
+ EXT4_MOUNT_SHOULD_DIOREAD_NOLOCK)
return 0;
if (!S_ISREG(inode->i_mode))
return 0;
@@ -507,9 +511,6 @@ static inline int ext4_should_dioread_nolock(struct inode *inode)
return 0;
if (ext4_should_journal_data(inode))
return 0;
- /* temporary fix to prevent generic/422 test failures */
- if (!test_opt(inode->i_sb, DELALLOC))
- return 0;
return 1;
}
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index fefcd42f34ea..bdf6b288aeff 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -6403,8 +6403,22 @@ static int __ext4_remount(struct fs_context *fc, struct super_block *sb)
}
+ /* Get the flag we really need to set/clear. */
+ ctx->mask_s_mount_opt &= sbi->s_mount_opt;
+ ctx->vals_s_mount_opt &= ~sbi->s_mount_opt;
+
+ /*
+ * If EXT4_MOUNT_SHOULD_DIOREAD_NOLOCK change on remount, we need
+ * to hold s_writepages_rwsem to avoid racing with writepages ops.
+ */
+ if (ctx_changed_mount_opt(ctx, EXT4_MOUNT_SHOULD_DIOREAD_NOLOCK))
+ percpu_down_write(&sbi->s_writepages_rwsem);
+
ext4_apply_options(fc, sb);
+ if (ctx_changed_mount_opt(ctx, EXT4_MOUNT_SHOULD_DIOREAD_NOLOCK))
+ percpu_up_write(&sbi->s_writepages_rwsem);
+
if ((old_opts.s_mount_opt & EXT4_MOUNT_JOURNAL_CHECKSUM) ^
test_opt(sb, JOURNAL_CHECKSUM)) {
ext4_msg(sb, KERN_ERR, "changing journal_checksum "
--
2.31.1
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